Re: [PATCH v2 3/3] PCI: ARM: add support for generic PCI host controller

[Jason Gunthorpe <jgunthorpe@obsidianresearch.com>]

On Wed, Feb 19, 2014 at 09:48:48PM +0100, Arnd Bergmann wrote:

> Hmm, we'll have to think about that. From a DT perspective, we try
> to keep things local to the node using it, so listing only the
> registers we are allowed to access is more natural.

If I understand the restriction properly, in a modern PCI-E world it
boils down to a limition on the configuration of each PCI-PCI root
port bridge (eg, a limited range of valid bus values, and apertures)

AFAIK it comes from the hidden per-socket routing registers that the
firwmare configures. Range X->Y (bus #, IO and MMIO) will be routed to
a specific physical socket, and then the PCI-E bridges in that socket
claim the transatcion based on their local config to select the
ultimate egress port.

So describing and restricting the bridge DT node itself, under a
single top level PCI domain stanza seems pretty reasonable.

As does containing the restrictions in a HW driver with knowledge of
the hidden registers, especially for firmware-less embedded. This is
part of what mvebu is doing already.

Jason